13 Oct
2015
13 Oct
'15
10:32 a.m.
On Oct 13, 2015, at 1:22 PM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
The Versatec electrostatic plotters are not the same as the VT52 printer, they are
yet another process. WIth those the paper passes between a set of electrodes that
build up a charge image on the paper. I beleive the paper is specially treated to
make it more resistive so the charge doesn't leak away too quickly, and there is
a clever multiplexing scheme for the electrodes to reduce the number of HV drivers
needed (IIRC there is around 600V between the electrodes on the 2 sides of the
paper.
The paper then passes over a stream of liquid toner, which is attracted to the charge
image. The liquid evaporates leaving the toner on the paper. That's it, no further
processing.
Speaking of Versatec: at University of Illinois, there was a PLATO terminal that had a
"Versatec screen printer". I never understood how that worked. It smelled like
the same electrostatic liquid toner technology. But how the image got from the terminal
to the printer is unclear. Remember that these were plasma panel displays, where the
graphics state exists only inside the gas pixels in the panel. I wonder if they read out
the on/off state of the pixels somehow, but how to do that when there's a 100 volt or
so square wave voltage across the panel is not obvious. I have never seen any
documentation of this machine.
paul