[Bdi4emc-help] Trajectory planner accel limits

Gene Heskett gene.heskett at verizon.net
Sat Feb 18 22:24:38 CET 2006

On Saturday 18 February 2006 15:12, mt0000 at sympatico.ca wrote:
>In my .ini, I have all of the acceleration parameters set to the same
> value, but these limits seem to be selectively violated by the
> trajectory planner.
>Using the bbxy.ngc file that ships with BDI, I plot the commanded
> X-axis velocity as the program finishes its initial X-axis move and
> turns 90 degrees to start the circle.
>At this corner the X-axis overshoot is first reversed by accelerating
> at about *twice* my set limits.  Then, it decelerates at the set
> limit to stop on the commanded position.
>Does anyone know under what conditions the trajectory planner will
> violate the accel limits in the .ini file, and by exactly how much? 
> If you could point me to the place in the code where this decision is
> made, that would be helpful.

I don't know if this is a 'datapoint' or not, but I looked at that with 
the halscope in emc2 testing, then looked at the code.  The code 
overshoots the starting positions starting radius of the circle by 1.5 
units, I assume as a chip clearing move possibly.  Looking at its 
traces with emc2 testing code, neither the initial move nor the 
reverseing at that point seemed to violate the maxvels set, the angle 
of the approach to the endpoint, there was a small radius in the trace 
as it turned around, then rose at exactly the mirror angle to the real 
starting point before the y motion was started.  I Plotted following 
errors too, for those I had to raise the gain into the microvolt range 
to see it at all.

So the code as it existed in testing 3 or 4 days ago seems to be nearly 
correct for this condition in that it was doing exactly what bbxy.ngc 
told it to do.  This 'TESTING' code I'm running ATM has little or no 
blending enabled at this time I've been told.  I do know that for a 
straight line but segmented move, I can hear the individual segments in 
the motor noises, almost as if its stopping between segments.  Blending 
would smooth that out a bit.

YMMV of course, I'm using steppers here, so I believe stepper_mod is the 
driver in use.

One thing thats not too clear to me is how I should translate the 
halscopes traces into something that would correspond to motion in 
seconds type of data.  The seconds is easy enough, but how does the 
displayed voltage trace translate in motion at the cutter?
Thanks, Gene

Cheers, Gene
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