Anders Wallin wrote:
> my recollection from a few years back is that the rigorous exact-stop mode is
> G61.1
> this stops at the end of *every* move.
>
> G61 improves slightly on this by "blending" moves where the
> end-tangent of the previous move matches the start-tangent of the next
> move.
> So with G61 there would be no stop with:
> G1X1
> G1X2
> (since we are continuing along the x-axis)
>   
Right.  Then, G64.1 Pxxx allows deviation from the commanded path to 
keep the speed up.
But, it apparently only looks ahead one line, and restricts velocity so 
it could stop at the
end of that line.  This is the safe thing to do, but it may not give 
enough speed in contouring
work.  There, they may fly along a path, perhaps parallel to the X axis, 
with small up/down
moves in Z.  At the end of the traverse, the speed could be slowed down 
to turn around and
go back in the other direction.  Speeds may be so high that the machine 
could not stop in
10 or 20 moves.  There are two options, I suppose.  Provide a different 
mode, where this
restriction is ignored, and the CAM is trusted to not ever exceed the 
machine acceleration
limits.  Or, develop an N-block look-ahead, and I know that can be QUITE 
complex.

This question comes up about once a year, I have essentially no 
experience in this
contouring area.  But, I can see that it is a bit of a shortcoming to 
those that do.

Jon

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