On Thu, Jan 05, 2012 at 10:37:35PM -0600, Jon Elson wrote:
> I just had somebody ask me about contouring performance of EMC2.
> I spotted something in the user manual I had never seen before, section
> 3.1.4, that says that no move can ever go fast enough that the machine
> cannot stop at the end of the move. This seems like it will significantly
> slow down contouring where many very short vectors occur in a row.
While this statement is true about the real-time trajectory planner, it
isn't the full story when it comes to contouring with emc.
If you have code that is of the "lots of very small segments" variety,
program G64 Pnnn or G64 Pnnn Qnnn.
http://linuxcnc.org/docs/2.4/html/gcode_main.html#sub:G61,-G61.1,-G64:
Either of these modes enables the "naive cam detector". When 2 or more
successive motions deviate from a straight line by less than the naive
cam tolerance, they are replaced by a single line from the start of the
first segment to the end of the last segment. There is presently a
hardcoded limit of 100 segments that can be connected in this way.
The algorithm is not precisely this one (because the method in emc is
not recursive, but decides after each segment is read whether it is
eligible for combination), but the illustration is good at understanding
why the concept works:
http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm
This combination happens in the task controller (source file
emccanon.cc), in case you're inclined to have a look at the code. Among
other things, this means that graphical previews like axis will not be
able to tell what segments are combined.
Reportedly this is fairly good at giving good contouring performance on
code out of typical cam software, as other posts in this thread have
observed.
This feature was first in v2.1.0, so it's been in there for quite a long
time.
Jeff
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