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Bill Noble[_2_]

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.70...
Mark Main fired this volley in news:d727636b-
:

That sounds *just* like an old hard drive
voice coil. ÿAnd by old, I mean 70's and
80's pre-winchester tech. ÿI've seen many
of them surplus, but not for about 10 years.

Those could do 5" of travel in about 40ms, with a 19oz head mechanism
(and that didn't count the weight of the voice coil, itself). It took
up to 30A to the voice coil at 48VDC.

I maintained those drives for many years, including doing mechanical
alignments, which encompassed things like adjusting the stop points
within 40 microns (to get the r/w head exactly centered between the
sync tracks on a standard calibration disk). They had elegantly-made
quadrature linear encoders as part of the positioning mechanism.

However, duplicating them from scratch is difficult. The originals -
say, Diablo (Xerox) Model 40 drives - had exquisite ball-bearing guide
rails for the assembly, with both vertical and horizontal bearing
elements.

That was partly because one didn't want any off-axis variations when
driving heads a few microns above a disk surface, and partly because
the gaps in the magnet assembly between poles and coil had to be in
the few (less than 10) thousanths to get the tight magnetic coupling
necessary to drive them that far, that fast.

I still have a couple of the ferrite magnets from such a head motor;
used with three strands of cord as a "parts finder" in the dirt floor
areas of my barn. G

LLoyd

for what it's worth, I picked up one of the Pertek drives at a swap meet a
while back cheaply - i wanted the rails it was mounted on - I cut the voice
coil actuator off of the cast base and have it handy if the need ever
arises.

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