Re: [CAD_CAM_EDM_DRO] Compumotor Plus stepper drive

hi Cary,

some resolvers do use brushes (they work against slip rings, not
commutators) to excite the rotor field. however to eliminate the brushes
entirely you often see a rotary transformer to couple the excitation
to the armature. this makes a brushless resolver a very reliable
component indeed. they can be used immersed in oil, dirt, and as noted in
your manual operate happily at high temperatures. they are used where no
other will operate (LED output goes way down at elevated temperatures, for
instance).

resolver systems don't compete favorably compared with optical encoders
when the encoders are up to the task. a large part of the resolver system
is the resolver-to-digital encoder which consists of quadrature analog
channels and the reference phase generator which must have low waveform
distortion for high accuracy. but for large machines such as a lathe for
ship drive shafts where it is impractical to re-zero an axis and an error
could destroy a very expensive part after weeks of machining, a nest of
resolvers, geared so each is within the resolution of the one above, can
give absolute position after a power failure. the cost of the resolver
system is a small part of such a machine.

i don't know the unit you have, but at Lawrence Berkeley Labs i saw an
application of a Compumotor drive (incorporated in a goniometric
photometer) which with no reduction gears, i.e. direct drive, with the
motor axis horizontal, moved heavy components at the end of a 1.5 meter
arm with just the bearings in the drive, brought cabling thru a 50 mm
central tube in the axis of the drive, while achieving accuracy of less
than a few arc seconds at speeds that could be slower than the rotational
speed of the earth. i didn't ask the price, but the government was able
to afford it. resolvers still have applications :-)

-ron

On Mon, 3 Jul 2000, Carey L. Culpepper wrote:

> Ron: Thanks for your reply. Here is what the user manual has to say
> about their resolver:
> A brushless resolver made of the same rotor and stator components used
> in the motor was developed. This resolver is magnetically similar to the
> motor itself, and is manufactured as an integral part of the motor. The
> result is a sensor with the same number of poles as the motor( which
> makes control straightforward) that is always properly aligned with the
> motor and can be operated in high noise, high temperature environments."
>
> This is what led me to believe that a motor might be wired to do the
> same thing.
>
>
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