Re: [CAD_CAM_EDM_DRO] Resolvers vs Encoders

We always used rotary brushless resolvers on machine tools which were
originally developed for the military and hence fairly robust. They have one
other advantage that they are absolute devices for one revolution. For most
applications full travel of the machine will be a few tens of revolutions.
We used the 2500Hz excitation frequency types and managed to get reasonably
good performance and accuracy.

The circuitry for using them is fairly simple using counters and comparators
to energise and extract the position.

Regards Peter

----- Original Message -----
From: <w.higdon@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, October 20, 2002 10:39 PM
Subject: Re: [CAD_CAM_EDM_DRO] Resolvers vs Encoders


> I'll try, altough Jon, could probaly do better.
> A resolver can be a transformer with a 2 or more phase
> primary. The secondary is inside the primary and is free
> to move, some are linear, and some are rotary. The
> Rotary ones usually use sliprings so the secondary can
> rotate through a full circle (360). Being a analog
> device the need something to convert them to digital.
> The chips are rather expensive now, when I worked at
> Entec, a new board cost between $500 to $1000 depending
> on accuracy. a encoder can either be a "Absolute
> encoder" (works just like a synchro with conversion
> built in). These are usually VERY expensive and limited
> in resloution. The second kind are "Incremental encoders"
> these output a series of pulses as they are moved. If
> they put out a pair of pulses streams with a phase
> difference between the pulse streams can be used to
> determine the direction of movement.
> Now that this is as clear as mud, I'll let Jon or
> someoone else clarify it.
> Bill Higdon
> PS you can convert a syncro machine to a eincremental
> encoder machine, by replacing the syncro's with suitable
> encoders. I did one upgrade (conversion)like that while
> at Entec.
> > Hi All:
> > Can any of you explain to me, the differences between resolvers and
> > encoders.
> > What is the implication for machine performance?
> > Is a retrofit from resolvers to encoders a worthwhile effort?
> > When did resolvers go out of favour and why?
> > I'm casting amorously about, for small CNC turning centers, and I've
heard
> > the terms mentioned, especially in regard to Hardinge machines.
> > Mid eighties machines seem to be the transition point from the resolver
> > system to the encoder system.
> > It looks to me like there is a fair amount of very nice old CNC iron
from
> > that era out there available for very little money...certainly far less
than
> > building from scratch or retrofitting a manual machine...especially when
you
> > consider that the enclosures, the coolant pumps, the ballscrews, the way
> > covers etc, etc are all already there.
> > Cheers
> >
> > Marcus
> >
> >
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> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this as a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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