What's that Lassie? You say that Joseph Gwinn fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Mon, 08 Dec 2008 11:08:34 -0500:

Many of the tracers that I've seen on the WWW, can trace a solid
silhouette.

How does that work?

I can think of a number of ways. One way has a 9-sensor grid and
detects edges, but I suspect that given the expense per sensor channel
back then, it wasn't done that way.

They may have servoed to a constant output (not zero) from the head, but
this requires knowing something about the orientation of the edge, which
is circular.

Ill think about it.

I think it would work similar to the line following rotating head, but
look for max contrast, not max balance, between a pair of photo cells.


--

Dan H.