Sensor for Detecting Stones

Well you have ground penetrating radar machines, or metal detectors which are considerably cheaper...Maybe if you tell us the purpose of this search we can pinpoint the proper tech....

https://en.wikipedia.org/wiki/Ground-penetrating_radar

https://en.wikipedia.org/wiki/Metal_detector

http://www.adv-geosci.net/24/69/2010/adgeo-24-69-2010.pdf

Sounds like a potato farmer to me.

https://en.wikipedia.org/wiki/Geotechnical_investigation

Are you asking about an optical sorting scheme?

https://en.wikipedia.org/wiki/Optical_sorting

I don't know if this would do what you want...

https://hackaday.io/project/4440-open-ground-penetrating-radar

If you're trying to separate potatoes from rocks, potatoes will float in salt water or sugar water. Most rocks will sink.

https://www.stevespanglerscience.com/blog/2008/10/23/potato-float-debate-alice-1059/

Wait, are we talking about in the ground or perhaps on a food processing conveyor line?

Due to lack of information, we're guessing!

Well in that case you need a field potato sorter....

http://www.foodproductiondaily.com/Processing/Tomra-spots-potato-processing-rot

https://en.wikipedia.org/wiki/Multispectral_image

I was talking about the ground, since I normally do not walk on a food conveyor belt, nor do I expect to step on a rock or a dog turd on one.

This particular application is for a conveyor belt which requires a different set of solutions and technologies.

Probably need to use the different mechanical properties of a potato and a stone to effect a detection, and trigger the separation, although floating seems to work pretty well. The Young's modulus of a potato is largely different from a quartzite stone. Thus, one could incorporate mechanical "fingers" (with rubber tips on them ??) to poke at all objects passing by on the conveyor. The ones that result in a sharp increase in pressure are stones (use a pressure sensitive transducer, as in a touch sensor), and the ones that have a lower pressure response must be either dirt clods or potatoes. Dirt clods might still be a different pressure signature from potatoes.

I would use a dual frequency ultra-sonic beam forming linear array. Migrant workers are much cheaper though.

If you can find them.....Idaho seems to be having a shortage...

http://www.potatogrower.com/2006/09/potato-growers-facing-labor-shortage

Power of the Spudnik baby....

Cool video...

https://www.youtube.com/watch?v=0KL7OrHkDaY

"Published online: Sep 13, 2006"

Any current news?

Yeah the Spudnik's have come to the rescue....

Rescued tubers await shipping....

The tater on the top is definitely stoned.

What is your budget?

What size veggies?

What size rocks?

Doesn't washing them remove the stones?

How about some information here!

"Spudnik" has been a brand of potato-handling machinery for many years, typically painted red as seen here. I once worked for a company that built other potato equipment like the white "Even-Flow" trucks in the video, each holding about 25 tons of potatoes. Eastern Washington rivals Idaho as a potato-growing area, and there are many potato sheds near where I now live.

Optical sensors are just about the best you can get. They are called Eyes! Signal is "Ahhhhh" for stone and "Ohh" for a veggie!

If you tell us what you are really trying to do we can be more specific. But I bet a potato sorting machine will not only help you detect the veggie but also sort it for you.

Years ago, I almost took a job working at the Westinghouse Navy Nuclear facility west of Idaho Falls. I remember the gal at the motel telling me that the town is not good for single men. If I was offered the job and accepted it, she recommended I live in Pocatello

Needless to say, I didn't take the job. I do remember seeing an ad for a big house (3500 to 4500 sq ft) on some piece of huge land (maybe 15 acres?). The property was all fenced in and the land was usable. The price was $199K!

Back to the topic. I remember having a decent dinner at the local steak house. Steak wasn't too good. The baked potato was amazing! It was huge, had a great fluffy texture and with only butter, it was delicious. I still remember how fluffy the potato was! A few years ago on a camping trip, I put some potatoes in aluminum foil and threw them on the grill (while cooking dinner). They were rock hard still, so I put the directly on the coals (still wrapped in foil) and they sat the entire night on the heat. The next morning, I remembered the potatoes and pulled them out of the coals (all gone by now). They were still warm, but they were rock hard. We gave it a shot and cracked one open - to our surprise, we had a delicious fluffy potato for breakfast. The skin and a thick layer of potato had become overcooked, so that had to be thrown out, but the core was delicious.

The OP is asking about detecting vegetables from rocks. I guess a potato is a vegetable, so is this what he's asking for help with? Of was this someone's assumption and we're all off track?

French fries are a vegetable, but baked potatoes are a meal unto themselves!

Another fast way to tell rocks from vegetables (actually tubers or roots) might involve some sort of microwave sensing, but the (illegal) field workers hair would all be permanently waved (quite tightly, I might add).

Vegetables float in water; stones don't. Does that help?

Stones have much higher hardness values than vegetables. Does that help?

Vegetables contain water; stones don't. Does that help?

Back up a it, and tell the forum what the size and shape of the problem actually is, before looking at sensors. To do so obviates the need for guesswork to answer a one-sentence specification.

Hi Everyone,

Thanks for the response.

We already have a cyclone water stone separator as seen in the video below.
https://www.youtube.com/watch?v=lWwS9KoVgSo
We are looking to now design a dry stone separator.
I have seen some on the market which they claim a "magnetic Actor Polarises the stones and clods"
I now have customers claiming it is not 100% accurate as if the clods are wet and the crop is wet it does not work as effectively.
So basically I am looking to scan all the crop moving across a conveyor belt and just detect a stone with a sensor.
Is there any way to do this?
Thanks for your help

Yes with different energy waves and sophisticated software you can sort satisfactorily...

https://en.wikipedia.org/wiki/Optical_sorting

http://www.ifrj.upm.edu.my/22%20(03)%202015/(2).pdf

http://tongengineering.com/product/agrisep-stone-clod-separator/

Why not try conditioning everything on the conveyor, say by subjecting it to infra red or micro waves and then use a temperature sensor to detect which items have a high water content and have absorbed heat i.e. veg, and which items that have a low water content so don't absorb heat i.e. stone.

Have you ever seen what happens to bulk precooked potatoes in transit? Actually, your idea is not a bad one at all. Ultrasonic reflectivity might also be different for stones vs. potatoes or beets or carrots based on plastic deformation characteristics.

Have you tried bare feet? Mine can typically tell the difference between a dirt clod and a dog turd.

This will take some knowledge about the characteristic size and shape of your undesirable stuff. Typically a sieve will separate junk from goods of the nature you described.

If that is not sufficient, you should know that burnt peanuts are separated from roasted peanuts at a rate of 10,000 per second using a vision system with air powered removal jets at a local peanut butter factory. Very impressive and very fast, but easy to detect with electronics based on color.

There are several inexpensive vision systems, such as that which Cognex offers, that can do blob analysis at a fast clip. Lighting is likely to play a key role in this case. If that seems plausible, upload a photo of the viewing area. Is it a conveyor? Just need a better idea of what you have to work with.