RE: [CAD_CAM_EDM_DRO] DRO Idea

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From: james owens [mailto:wotisname@...]

Another idea could use a laser read head from a CDROM, these are ten a penny
with every week bringing out a bigger and faster model. Here again is a
problem of obtaining CD's as a strip to make the encoder.

James, the CDROM read head floats on a magnetically controlled pivot (axis)
so that it may adjust for the fact that the CDROM track it must follow is
often slightly off center. The read head then adjusts itself to follow the
tracks 360 degree variations. This is not to be confused with the servo
position system which moves the entire read head assembly over the entire
CDROM. This design makes the CDROM read head work very well for its intended
purpose, however they are sensitive to vibration. I suppose, you could lock
the head so that it may not move and borrow the optics, emitter, sender and
beam splitter for the task at hand. In samples I observed, there was no
feedback to maintain emitter intensity. The split beam topology has a clear
advantage in that the target has little paralax issues or problems with
changes in distace between the sender and receiver (since the path of the
emitter and receiver beams are the same and are split with a right angle
glass window). I don't think anyone who takes this on will uncover much
useful interface electronics in a CDROM. It appears that the wiring for the
emitter and sender are easy to reach, and the entire head assebly looks like
it can be removed without much difficulty. I do no not know what sort of
resolution, beam width, and so on is possible. It is a well engineered piece
of work.

One must appreciate that after you go to all this trouble you have come full
circle the hard way, becuase you are right back at glass scale kind of
stuff, except you can reflect a beam rather than pass one though the scale.
Worse, you don't have a scale to bounce your beam off of. Time and cost you
may end up 0 for 2.

David R. Howland