> The closest analogy I could give would be a door and a rubber doorstop, a=
lthough my
> application is vertical. The permanent magnet is on the door and the EM i=
s the
> doorstop. My hope was to detect the approach of the 'door', probably with=
 either a
> Hall Effect chip, or maybe even an induced voltage in the EM, and energis=
e the EM to
> prevent a hard collision. After which the field could be reduced with low=
 frequency
> PWM (as the core will be slow-to-react iron) to allow soft contact

Would it be enough to have an un-energised electromagnet, and short the end=
s of the winding together, so the induced current causes a back electromagn=
etic field? Probably work better with pole pieces on both items designed to=
 form a more complete magnetic circuit than a disc magnet.
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