Re: encoder head pitch, or, quit your griping.

Hi,

A number of measuring systems I have seen use the Moire effect - is this
a tecnique which might be used to overcome the lack of a suitable pitch
grating? As I remember, two gratings are used mounted at a slight angle
to each other. this has the effect of producing strong dark bands moving
at right angles to the lines of the grating and allowing finer
measurement from relatively coarse gratings. The angle at which the
gratings are set affects the width of the bands and IIRC a smaller angle
increases resolution - or have I got it all wrong?
The kind of system I envisage would be easily made on the mechanical
side and would consist of a tape with a number of straight black lines
running the length of the machine - say ten at any even spacing - and a
reading head incorporating another strip of the same kind of stuff and
say ten IR phototransistors looking through the crossed gratings via
small slits in a metal plate. I think that by choosing the number of
lines, the grating angle and the number of phototransistors to give an
accurate repeat rate, it should be possible to achieve good resolution
by simple means. The grating could proboably be made by dragging a strip
of acetate across the cutting adge of a screw tap in a suitable frame.
Obviously, the electronics would have to discriminate
which of the Phototrannies was dark and interpret this into a
measurement but I'm sure this shouldn't be too difficult to achieve. I
haven't tried this as I'm working too hard on my CNC
mill but I'd be interested to hear your views.

Ian

> Mouse electronics count fringes. A serial port mouse sends the position
> data to the computer when inquired or when state changes. I wonder if these
> could be adapted to DRO's?

Best wishes

Ian

--

Ian W. Wright LBHI
Sheffield Branch Chairman of the British Horological Institute.
Bandmaster and Euphonium player of the Hathersage Brass Band. UK.
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