Re: BDI and servos

>    From: Bob Simon <bsimon@...>
> Subject: BDI and servos
>
> Can the Brain Dead Install of EMC be used with analog servo systems or
> is it specifically set up for step and direction only?

You can use the EMC (BDI includes a full EMC) to drive either stepper or
servo motors. The choice is made by a single variable in the ini file
that is read during startup. It is also easily possible to write
multiple personalities for the EMC on a single machine and start any
using a single command or icon. (if you are a point-n-click kinda person
and set it up that way)

In the case of full servo control by the PC, in contrast to step and
direction servo control like Gecko 3xx or 4xx amps, you'll need a board
or board set that will make the analog(ue) signals that will drive the
amps. With a servo driver software module like stgmod you have ini file
control of max and min voltage and zero or bias as some call it. You
will also have a full PID loop with the usual feed forward computations.

I saw a demo of a mill that ran with either the usual velocity control
from the EMC or current control using the same computations. The
velocity control included amps that used tach signals for speed feedback
while the current loop ignored the tach signals and used position
computation right out of the PC. I couldn't tell the difference in
control of the motors during accel/decel or during smooth motion at most
any speed. But having said this I have to say that the guy that did the
demo had some pretty sophisticated proprietary tuning routines and knew
how to use them.

You will also need something to read the encoders for position. There
are a few companies that make combination boards for both these sets of
signals. The most common is the Servo-To-Go but more recently the EMC
developers have added Vigilant and are working on Studio Ferraris. An
interesting alternative to the PC cards is Jon Elson's (PICO) parallel
port motion control board sets.

HTH

Ray

FYI - I have a tiny vested interest in PICO's servo boards. I sell the
BDI disks for about a 1% profit. I have a HUGE interest/investment in
the EMC.