How can I detect metal contact on u shaped electromagnet and register that contact to an Arduino?

#12

Joined Nov 30, 2010
18,224
Telling the difference between a few tens of micrometers will be difficult differentiating from true contact.
Let me use different words for that: A layer of dust, a few grains of sand, a piece of paper, will make almost zero difference in detecting what seems to be actual contact. As the plate gets within about a half a millimeter, the current will change, a lot, and that's easy to detect.
 

GopherT

Joined Nov 23, 2012
8,009
What do you mean? Is it not possible to build an EM that will alway let go when power is cut?
If you have the right non-magnetizable steel. The longer you leave a magnetic field near most iron alloys, the more magnetic it will become. Swipe a sewing needle on a magnet, set it on a floating cork and you have a compass.
 

Thread Starter

Michael Campbell

Joined Oct 25, 2015
36
Let me use different words for that: A layer of dust, a few grains of sand, a piece of paper, will make almost zero difference in detecting what seems to be actual contact. As the plate gets within about a half a millimeter, the current will change, a lot, and that's easy to detect.
That works for me. I'm just wondering about detection if it's there for only a millisecond or two. Can that be registered to an arduino?
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
When you lift with a DC electromagnet, on switch off there is residual magnetization that can retain the object, the traditional method is to give a short pulse in the reverse polarity to release.
H bridge control electronic or relay.
The solid iron core is a little more efficient on DC.
Here is one I have used in the past.
Max.
 

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Thread Starter

Michael Campbell

Joined Oct 25, 2015
36
If you have the right non-magnetizable steel. The longer you leave a magnetic field near most iron alloys, the more magnetic it will become.

If you have the right non-magnetizable steel. The longer you leave a magnetic field near most iron alloys, the more magnetic it will become. Swipe a sewing needle on a magnet, set it on a floating cork and you have a compass.

Ahhh! I wasn't aware of that property. I though I had a short or something. That makes perfect sense now.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Another reaction if continuous use heats the electro-magnet, it loses strength and in some cases lose effective lift capability completely for some heavy materials.
Max.
 

Thread Starter

Michael Campbell

Joined Oct 25, 2015
36
When you lift with a DC electromagnet, on switch off there is residual magnetization that can retain the object, the traditional method is to give a short pulse in the reverse polarity to release.
H bridge control electronic or relay.
The solid iron core is a little more efficient on DC.
Here is one I have used in the past.
Max.
Yes, I've played with these before. They're super strong, but I can't seem to get the same flux properties of the U shaped mags, meaning, the flux field on the round mags have 90% of their strength right on contact, with little left further away. The Us seem to spread it out a little more, pushing the flux field much further away, good for my application.
 

Thread Starter

Michael Campbell

Joined Oct 25, 2015
36
If you have the right non-magnetizable steel. The longer you leave a magnetic field near most iron alloys, the more magnetic it will become. Swipe a sewing needle on a magnet, set it on a floating cork and you have a compass.
So, how long does it stay magnetized?

Now I'm trying to figure out if I should get a non-magnetizable steel or just go for the magnetized steel and introduce an h-bridge. I can see some power management upsides with the magnetized steel if I can depend on it always being magnetized.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Depending on if you need to go for maximum efficiency, the soft iron core has the most.
How long does it stay magnetized?
I have worked with scrap yard magnets that draw 100amps, if the reverse pulse is not used, the lighter objects lifted will stay attracted for hours, if not demag'd.
Max.
 

mcgyvr

Joined Oct 15, 2009
5,394
Just detect the presence with a microswitch to pull an arduino pin to ground

Vacuum/cup pickup eliminates any issues with magnets too..
 
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