DRO

Hello:

I talked to RSF Electronics (Elektronik) about a surplus linear encoder I
picked up. In conversation I found out it's replacement cost (I was
curious), although it's discontinued and only sold as replacment stock, and
also got a catalog.

In the catalog I noticed they have an 'open' scale & head unit, which I
imagine costs less. The enclosed one I have has 25 lines/mm with 5x
interpolation, which gives 125 lines/mm pre-quadrature or 500 pulses/mm
post-quadrature (pre- and post- were RSF's choice of language), for 0.002 mm
resolution (20 um). They make a 10 um also (perhaps make inch calibration
also). List price for the 270 mm enclosed one with dust/debris trap etc is
$600 or so.

I would think the open one would be less, but sounds like some of you need
alot longer length, so maybe there's no bargain to be found here.

I'm looking at the HP HCTL-2016 quadrature counter chip (16 bit binary
counter) to 'handle' the data, at a cost of about $10.71
(www.future-active.com ), but realized something has to convert counts to
position, same problem as with rotary to linear translation...meaning some
intelligence (PIC, PC, whatever).

Here's a thought I haven't completed. If it's valid, I wonder if it's useful
to people doing the programming side of developing a DRO. For metric users,
a system that gives 500 pulses/mm is only 'off' by a factor of two for
position correlating to count, ignoring decimal point for the time being. If
I remember right, multiplication and division in binary can be accomplished
by a shift register....shifting one bit = x2 or /2. In the right direction,
this could make the count and position correlate, although it might also
mean a loss of one digit resolution (power of ten). If ti works, it could be
done with display logic and no cpu.

This could be a case of a little knowledge being dangerous, and it's also
useless with inch calibration with other encoder resolutions because the
ratios aren't so 'clean'

I may have missed earlier mention of the HP chips in the tide of DRO trafic
on the list. If it hasn't been discussed, I hope this was helpful.

Murray