On Thu, Jun 04, 2009 at 01:15:01PM +0200, Jasiel Nájera wrote:
> Hello to everybody.
>
> My questions are:
>
> 1- Is it posible to implement other types of controllers instead of PID?
> If so, have some of you already done something regarding this?
> I'm thinking on designing a compesator with QFT Robust Control, but the
> problem is that the only compensator structure I find is PID, neither PI-D.
If you want another kind of "controller", write it as a HAL realtime
component.
About the syntax of comps:
http://linuxcnc.org/docview/html/hal_comp.html
About compiling your own comps on your own system (section 1.3)
http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?ContributedComponents
I am not familiar with the specifics of "QFT Robust Control", but the
emc motion controller really works very simply when it comes to
commanding motor positions:
Every servo period (typically 1ms) the realtime motion controller reads
the motor's feedback position (e.g., from axis.0.motor-pos-fb) and if it
is too far from the commanded position, it signals an error. then it
computes a new commanded motor position and outputs it (e.g., on
axis.0.motor-pos-cmd).
What is done after this depends on the type of systems: on simulated
systems without real hardware, motor-pos-cmd is simply connected to
motor-pos-fb. On stepper systems, a pretuned loop uses velocity and
error to control a frequency generator; the new feedback position is the
old position plus the number of steps generated during the last period.
On a PID servo system the command and feedback are used to compute a
value that goes to a servo amplifier.
Based on the little bit about QFT I could find not behind a paywall, it
sounds like it's broadly similar to PID in terms of its inputs and
outputs (but different in terms of the tuning parameters and computation
method); if you understand the QFT algorithm then it's mostly a matter
of transcribing the algorithm in to the subset of C that is available
for realtime components, arranging for the tuning parameters to be
set, and modifying a PID-servo hal configuration to use QFT instead of
PID.
We'd be interested in hearing about your results.
Jeff
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