Re: [CAD_CAM_EDM_DRO] Resolvers vs Encoders

Marcus & Eva wrote:

>Hi All:
> Can any of you explain to me, the differences between resolvers and
>encoders.
>

Resolvers use varying magnetic coupling to provide signals which vary in
amplitude (and have
a sign, ie. + or - phase relationship). A sine wave excitation is
applied to one winding, and
sine waves are produced on 2 other windings, which vary in amplitude as
the resolver is rotated.
Interpolation is used to obtain higher resolution information than the
raw quadrature cycles
inherent in the output.

Most encoders today are optical, with LED light sources. back in the
days before LEDs,
encoders were considered unreliable, because the light bulbs would burn
out. Most encoders
in modest systems, especially home CNC systems, are used at their
inherent resolution, and
not interpolated.

>What is the implication for machine performance?
>

Not much. but, a device to read out position from a resolver is more
expensive, maybe
MUCH more expensive, than what is needed to read position from an encoder

>Is a retrofit from resolvers to encoders a worthwhile effort?
>
>

I did it on my machine. So, yes, I'd consider it worthwhile.

>When did resolvers go out of favour and why?
>
>

I don't know if they are "out of style", as some large machine builders
still use them.

>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.
>
>

Certainly. Don't let a resolver-equipped machine scare you off. It
will probably be cheaper
to retrofit with encoders as part of the CNC controller retrofit. It is
possible that there are
black-box resolver converters in the CNC machine that can be used with
the new controller,
though. If so, then you would not need to pull the resolvers.

Jon