Accuracy of Step/Dir Driven Brushless Servos

I sent you a private email where I answered at least
part of your question. I'll try again.

You do need to connect the encoder a and b phase
outputs to both drive and rutex. Obviously, you only
need to power the encoder from one source.

In general, if an brushless servo motor drive has an
encoder input, it uses it for commutating the motor.
The rutex needs the encoder output to close the
position loop, i.e. each time it gets a step command,
that is the same as a change in position. It then
changes the voltage as required to make the motor
match that new requested position. The drive is using
the encoder output to make sure that it has changed
position enough to meet the new demanded position that
it is getting from the rutex, plus it needs that
information to know how to commutate the motor.

Having said that, I have a Compumotor OEM650SD that is
simply a hall commutated torque command drive with an
added board that does exactly what the rutex board
does. I believe this technique is quite common,
although I am hard pressed to think of another example
right now.

So the simple answer is that brushless drives,
properly tuned, are able to respond to fairly small
position input commands, like a step/direction
controller would request.

My backup plan for my bridgeport is to use step/dir
inputs to my brushless drives. I don't think that
there are any significant accuracy issues with this
setup.

Eric






Is this a stupid question or something? I am curious
why no one has
responded.
Mark

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "natchamp_87
<mark@h...>"
<mark@h...> wrote:

> I really need some input. Does anyone have any

experience with

> driving brushless servo motors with Step/Dir

signals? My plan is
to

> use the Rutex 997 board that inputs step/dir signals

from the

> parallel port and outputs the 0-10v signal to my

Aerotech drives.

> The Rutex board also receives encoder feedback. My

question is: Am
I

> sacrificing accuracy with this approach? (or

anything else?) Also,

> will my encoder feedback go to both the Rutex board

as well as the

> drive/amp because the amp has encoder input too.

Any feedback

> greatly appreciated!
>
> Mark

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com