Re: True servo system with STG cards

Hello,

STG = Servos To Go (A manufacturer of a board used with EMC to read
encoders and close the servo loop TO THE COMPUTER for "true" servo
control. About 800 bucks, AIRC.)

What is nowadays called TRUE servo simply means that the feedback
loop essential for ALL servo types, is closed TO the computer.

A gecko IS a "true" servo in that it HAS a feedback loop. But in this
terminology, it is not a TRUE servo because it closes the loop to
itself, rather than the controlling computer.

Sounds like double talk, and it is in some respects. But a "step-
servo" like the Gecko or Rutex has many of the advantages of a TRUE
servo arrangement, with less cost and often easier setup and
maintennance.

The largest down side to a step servo, compared to a TRUE servo: If
one of several step servo controlled axes is slowed by an obstruction
or by exceeding their physical motion capability, the OTHER axes keep
moving as if nothing is wrong. The toolpath will not be correct due
to this, even though "servos" are being used. With a TRUE servo
setup, the computer will recognise that one axis has slowed, and slow
all the other axes proportionally to maintain an accurate toolpath.

It's intersting to point out that the intended operation for the
Gecko G200x will actually allow it to perform as a TRUE servo setup
even using STEPPERS (or step-servos). This is due to its being not
only the source of the pulse trains driving the axes, but also its
having an onboard intelligence equal--superior-- to that which closed
TRUE servo loops in years past.

It's a GREAT time to be involved in CNC!<G>

Ballendo


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "shadi_salhab_78"
<salhab@m...> wrote:

>
> Hi all,
>
> I have been looking for EMC requirerments and I faced this "True
> servo system with STG cards" what is a STG card ? and what is meant
> by the word "True "? Is the gecko pulse and direction servo is not
> True?
> Thanks.