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Opposing magnets, how to minimize off axis force?
3

thread340-190723

Opposing magnets, how to minimize off axis force?

Opposing magnets, how to minimize off axis force?

(OP)

We have a device that uses opposing magnets to transfer force from an object to a sensor.  The object is attached to a ring magnet. The ring magnet is kept in its vertical axis through a guide rod. The other magnet, a disc magnet, is attached to a sensor.  

The problem is:  the off-axis force or side load force on the ring magnet is causing stiction between the guide rod and the ring magnet.

Any ideas on how to minimize this force? Can we modify the sizes of the magnets, however, if the ring magnet ID is made too large, it will attract the disc magnet rather than oppose it.

Thanks in advance,
Greg

RE: Opposing magnets, how to minimize off axis force?

Is the guide rod magnetic (steel)?

RE: Opposing magnets, how to minimize off axis force?

(OP)
Thanks, to answer your questions: the guide rod is non magnetic.
-Greg

RE: Opposing magnets, how to minimize off axis force?

That may be a tough one.  Since there are no stable arrangements for levitating magnets, I suspect that the ring magnet is trying to flip to the stable arangement (North to South pole).  This torque is likely to be proportional to the replusion force.

Can you make the guide rod (and the ID of the ring magnet) have less friction by using low friction coatings?

RE: Opposing magnets, how to minimize off axis force?

To me your challenge seems similar to levitating.

You want repulsion, axial centering, and resistance to tipping.

Earnshaw's theorem says it can't be done (except perhaps a few loopholes.)

How about mechanical means to bevel/smooth the i.d. of the ring magnet so it doesn't bind, or lubricate those surfaces.

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RE: Opposing magnets, how to minimize off axis force?

(OP)
Thank you, yes you are right. The magnet is trying to flip over.  We can play with low friction coatings and modified surface geometries to reduce contact area.  

-Greg

RE: Opposing magnets, how to minimize off axis force?

The systems that I have seen that used this all had a non-magnetic bushing in the center of the ring magnet.  This let them control the bearing surface.  I would suggest brass for the bushing and rod.  A soft grade for the bushing and a harder one for the rod.
You could use plastics for the bearings, but when they get nicked they tend to stick.

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