Encoder

[dn]

Andrew Dalgleish wrote:

> Photo reduction isn't that expensive. I've done it by taking a shot with   
> a 120 camera and using the negative. Most wedding photographers could do   
> it for you, probably for a few beers.

You can't just use ordinary film for this type of work.  It's way too grainy
and imprecise for precision photo reduction.  The film must be an ultra slow
very high contrast film, used to be used a lot for printed circuit board
artwork and photolithography.  Also, to get precise reduction of the artwork,
a very expensive and accurate bellows type camera with precision dolly is 
necessary.  You need exactly X:1 reduction if the finished product is going 
to have the exact line widths and precise, sharp edges you need for an 
encoder.  Just not the type of stuff Weddings'R'Us is going to have lying 
around.
 
> I've also seen a sticky metalic (so it doesn't stretch) tape with   
> light/dark bands on it. You just wrap this around a shaft a few times   
> until the stripes line up.

This would be ok for low res (a few pulses per revolution), but it would
be nearly impossible to get it synched up exactly with the camshaft position,
which you'd need for an engine controller.

> That's less than 28 hours at 6000 rpm. Are you sure there isn't another   
> 1000 in there?

When was the last time you saw a Briggs + Stratton doing 6000 RPM?  

> Sounds a *lot* better than using separate led/phototransistor.

Still doesn't beat someone else doing all the hard stuff, + you just go down
to your local supplier and pick one up.  The pickup is the easy part, the
optical disk is the black art...

regards
dn


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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
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