To: Members And Friends
NFB R&D Committee
From: T. V. Cranmer, Chairman
Subject: Spur wheel plotter
Date: November 15, 1994
Abe's observation that a spur wheel drawing is superior to graphs
produced on a braille embosser echoes my experience, and I believe
that of our Committee. Mike Freeman says "let's build it."
My first thought was that we should be able to modify a pen-based
plotter. I called Mike Romeo, the smartest design engineer that I
personally know, to get his opinion on this matter. Here are a few
of his reactions:
It will take a lot more mechanical force to guide and emboss with
a spur wheel than it does with a pen.
Should the spur wheel move? Should the paper beneath the wheel
move? Or should both move?
It probably won't be possible to emboss lines with acute angles
without halting the travel of the wheel, reducing or minimizing
down pressure, rotating the wheel to the desired angle of travel,
restoring down pressure and resuming wheel travel. This level of
control is not impossible, but it clearly poses a software as well
as a mechanical design challenge.
Executing smooth curves should be easy--if the curves are not too
tight. How tight is too tight? At some point, perhaps encountered
in drawing cursive writing for example, it could be necessary to
resort to the stop-and-go motion required for making acute angles.
What cushion material should be used beneath the paper? Natural
rubber mats have a short life expectancy. Many synthetic rubbers
are too hard, some are prone to slicing or dimpling. How would a
firm felt pad work? Does anybody know, or have a well based
opinion, of a good material for this application?
What paper size should our automated wheel plotter accommodate?
Mechanical forces produced by drawing will increase rapidly as the
length of the arm holding the wheel increases.
There are other concerns that we now vaguely perceive. We are
always plagued by the cost factor. Should we build a magnificent
prototype that would require hundreds of thousands of dollars to
tool-up for manufacturing? How much attention should a research
group give to such questions?
I'm sending Romeo a spur wheel, a few mats of different materials,
and a copy of this memo. (Mike already has plenty paper.) He and
I will stay in touch, while awaiting your opinions and suggestions.
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