Ned Simmons wrote:

On Wed, 29 Apr 2009 12:35:02 -0500, "Pete C."
wrote:


Ned Simmons wrote:

On Wed, 29 Apr 2009 12:17:06 -0500, "Pete C."
wrote:


Karl Townsend wrote:


You haven't looked closely enough then.

No closed loop servo control,

Closed loop servo is indeed available. Servo drives such as the Geckos
are closed loop and will readily fault and halt Mach3 in the event the
servo error exceeds the set threshold, just like any other servo system.

The Geckos are a kluge that allows you to run servo motors from the
step and direction signals more commonly used for driving steppers.
Convenient under the right circumstances, but you'd sacrifice quite a
lot of the functionality that the Galil controller offers by going
that route.

What functionality? It's still closed loop, still flags an error and
shuts down the control if the servo is overloaded and can't hold
position, you can still tune the parameters, etc. I can't think of any
feature you loose that is relevant for the class of control.

The first thing you'd lose is the Galil controller itself, unless it's
a newer card than what I imagine it is. Some of Galil's newer
controllers can be configured for either step & direction or +/-10V,
but not the older generations.

But setting that aside, the first couple things that occur to me are,
since the gains are now set in the amp rather than the controller,
you'd give up: the auto-tuning routines available for the controller;
the ability to replace a drive without going thru a manual tuning
process(with the Galil board the setup parameters can be stored in the
motion program); and the ability to change the loop gains on the fly
in software. Also, the Gecko is missing integral gain.

Unless you were able to set up a second feedback loop from the encoder
to the controller board, you wouldn't get the "digital 'scope"
utilities that Galil supplies, and the motion program wouldn't have
access to real position and velocity numbers.

Ok, and exactly how relevant are those features to the day to day
operation of this class of machine? We're talking old used retrofitted
iron here, not the latest $1M machining centers. Nearly all of what you
indicated is only relevant to one time setup. I believe Mach3 can also
read encoder positions in some configurations so it does get to see the
"real" position, but even so, that makes little difference for this
class of control and machine. You're trying to put a Ferrari engine in a
Chevy truck.