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Joseph Gwinn

In article ,
(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.

The classic approach is two photocells (or one split photocell) feeding
a differential amplifier. If the line is halfway between the cells,
output is zero. It the line strays one way the output is negative, and
the other way positive. To do full X-Y, there will be four cells in a
square, and two differential amplifiers.

This was enough for the gantry servo to steer by.

Although it was easily distracted, as other posters have noted.

Joe Gwinn