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Hi Adrian,
Why not use a linear servo motor?
Those have a plunger you can control to the
hilt.
Also, if you energize a solenoid with a current
amplifier you can get more control. (Watch for "shorted turns" in the permeable
steel frame, if any - those should be eliminated, or slit so they are no longer
a closed loop).
Most solenoids are energized with a certain
"voltage", or fed by a voltage amplifier (ie, the output voltage is some
multiple of the input signal but the amplifier doesn't care about the current
it's sourcing, below some overload limit.)
Since magnetic fields are of course proportional
to current, you can use a current amp (ie, the output currentis
some multiple of the input signal, but the amplifier doesn't care about the
voltage it's sourcing to get that current, at least within its own compliance
headroom.)
This gives you way more control.
It's also one primary reason why some folksendure
the hassle and expense of vacuum tube audio amplifiers (As opposed to solid
state) - tube amps are current amplifiers, and solid state amps are
voltage amplifiers. Doesn't make much sense to me - if the force on a
speaker cone is proportional to the current through the voice coil, why
are we usually driving it with a voltage amplifier!!?
Graham G.
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