13 Jan
2011
13 Jan
'11
11:28 p.m.
On 2011 Jan 13, at 10:59 PM, Fred Cisin wrote:
Spiral in the disc drive, but I think Philip is drawing an analogy to
the mechanism in digital cameras that moves the lens in and out and
does the zoom. These are concentric cylinders with pins in one cylinder
riding in helical grooves in an adjacent cylinder. I think the point is
in both cases the objective is to transform rotational motion (easy to
generate with a small motor) into linear motion (arguably more
difficult to generate directly).
Mathematically, I think a helix and spiral can be shown to be
topologically equivalent, at least as long there is a hole in the
center of the disc with the spiral (imagine expanding the hole, folding
the surface of the disc out to become the cylinder wall: one side of
the disc becomes the outside of the cylinder, the other side becomes
the inside, and the spiral turns into a helix).
(Fixed a digital camera for a friend awhile ago which had been dropped
with the lens extended. Had to be disassmebled extensively, to find one
of the guide pins had been knocked out and was jammed between the
cylinder walls.)
> I don;t
think they're any worse than other disk drives. And a lot
> better
> than that darn Shugart thing with the spirally-gooved plastic disk to
> move the hean. ARGH!
On Fri, 14 Jan 2011, Philip Pemberton wrote:
Sounds a bit like the helicoid in a camera
lens...
Flat disc with a spiral, NOT a helix. Used in the Shugart SA400. Just
like a primitive music storage system that was called a "record".