On 20.04.12 12:25, Jon Elson wrote:
> Stuart Stevenson wrote:
> > Doesn't even G02/G03 result in a series of very small linear moves sent to
> > the servo motors? Wouldn't a NURB conversion do the same thing
>
> Yes, in a way. But, the G02/G03 is known to be a single move, so
> there is no velocity change until the end of that move. NURBS doesn't
> really solve this problem, it just condenses the description of the
> surface, and allows a program to fairly simply determine the
> accelerations that might be needed to traverse it.
>
> The problem with general G-code is each block tells you nothing about
> any other block. So, you have to read arbitrarily far ahead to know
> if there are any sudden changes in velocity coming up.
Sort of arbitrary, but fully determined by the gcode, I think, because
the look-ahead only needs to keep one stopping distance ahead of the
executed motion, by subtracting the length of the currently executing
motion, and adding enough look-ahead segment lengths to stay far enough
ahead for the current feedrate. If there are no sharp bends or a stop in
the headlights, keep truckin'.
I don't imagine that we sprinkle so many feedrate changes into the
segment list for a G1, that Mach's merging of the next feedrate would
make a damn's worth of difference to this case. Our problem is getting
LinuxCNC off its knees, to dare to obey the given feedrate on a long
chain of micro-segments. (I.e. fit headlights, rather than have a man
with a red flag walking in front.)
Erik
--
Re: Graphics:
A picture is worth 10K words -- but only those to describe the picture.
Hardly any sets of 10K words can be adequately described with pictures.
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