dan wrote:

how do those optical pattern tracers follow a line?

I saw an old one back about 20 years ago. I don't think that it had
any "high tech" stuff like CCD cameras or digital controls.
Servos maybe. The one I saw had an 'eye' that would turn as it went
around the pattern.

Any one know how they worked. And how the tracer controlled the speed
of the X and Y drive motors to maintain speed at the torch as it went
around.




It has been quite a while since I worked on an optical tracer head. It
had some miniture lamps the illumininated the line, I think there were
four of them around the bottom of the tracing head. There was a mirror
that was rotated by a motor that directed the focused image of the line
onto two sensors. There was a magnet on the rotating shaft that held the
mirror that gave the angular position of the mirror. Each axis was a
separate circuit and as the mirror would scan across the line, first
from left to right and then right to left the sum of the two scans was
fed into the amp for the servo drive motor. If the head was drifting to
the right the combinded reference voltage would go higher and move the
head to the left and vice versa. The same action operated the other
axis. The speed of the cut was regulated by a control the set the gains
of both amps.


John