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. ------------------------------------------------------------------------------ For Developers, A Lot Can Happen In A Second. Boundary is the first to Know...and Tell You. Monitor Your Applications in Ultra-Fine Resolution. Try it FREE! http://p.sf.net/sfu/Boundary-d2dvs2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users