Re: stepper vs servo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> ddgman2001 wrote:
>
> >If the feedback goes to the gecko unit, how well does it handle
> >error compensation?
> >
> >
> What is error compensation? Since it is an open-loop system, the
CNC
> computer has no idea how close the actual position is to the
commanded
> position, ather than knowing it is within 128 encoder counts, as
exceeding
> that will cause the gecko servo to fault. Within the 128 counts, a
PID
> (Proportional, Integral, Derivative) feedback control loop is
implemented
> in hardware to give stable and smooth following of the commanded
> position.
>
> Do you mean compensation for backlash? That can still be handled
in the
> software.
>
> Do you mean feed rate compansation
> (slowing down all other axes to accomdate one axis that is lagging
behind)?
> With no feedback to the CNC control, that can't be done.
>
> Do you mean machine error compensation? That is done by a table in
> the CNC control's memory, that knows how many thousandths to add
> or subtract for certain ranges of position of each axis. That can
still
> be done in software.
>
> Jon