16 Jun
2015
16 Jun
'15
12:20 p.m.
And yet another (possibly the most common one on
computers) is to have a
small drive wheel that pulls the tape at constant speed across the
heads, and then have some other construction that drives the tape reels
depending on tape tension or length. Think vacuum columns or spring
loaded arms.
That is closely related to the capstan and weakly-driven take up spool I think. The actual tape movement as such, is all done by the
small wheel next to
the head, which just runs the tape past the head.
Which is essentailly the same as the capstan in an audio tape recorder, albeit the
computer
drive doesn't have a pinch roller
I've been wondering if there is some sensor of
tape tension/pressure at
the heads, and this will allow the drive to figure out how much
faster/slower the reels must run, relative to each other, in order to
keep the tape tensioned. Then you can figure out tape speed across the
heads (if you care) by just observing flux changes.
Only if there is something on the tape. These computer tape drives could surely record on
a
totally blank tape and get the right number of bits per inch. So the thing can't use
the data rate
at the head as a speed measurement.
One of my VHS
video recorders does something similar to work out how much recording space is
left on the cassette.
That can't be very precise... :-)