On 21.04.12 23:23, Jon Elson wrote: > Viesturs Lācis wrote: > > What I see the big issue for solving this in trajectory planner or > > whatever _inside_ LinuxCNC is that I do not see, how to determine by > > some hard facts, what is the best way to determine the lookup amount. > > > The number of blocks you need to look ahead is variable. The way I > imagine it, you'd look ahead until you found a move that violates the > requested speed due to acceleration. Then, you have to work backwards > from that point to find out what block you need to begin slowing down > at.
Jon, there's probably no need to do this backwards. Look-ahead only needs to be simple look-ahead, nothing more, AIUI. The current velocity (feedrate) is known, and the stopping distance for the machine at that velocity is fixed. So, by summing immediately upcoming gcode path segments to a length a little greater than the stopping distance, LinuxCNC can _safely_ continue at full feedrate in the currently executing path segment if there are no sharp bends or stops in the look-ahead "headlights" zone of scanned path segments. If there's a sharp manoeuvre showing in the headlights: drop feedrate below that gcoded for the executing segment, according to the deceleration needed for the impending path deviation. So the look-ahead is simple. If there's any complexity thus far, or need to do it backwards, then I'm having trouble seeing it, and would appreciate enlightenment. The memory required to queue even a thousand coordinate points of a long G1 path is so miniscule in relation to current RAM stick sizes, as to be completely negligible, I think. Erik -- Bumper sticker: Honk if you love peace and quiet. ------------------------------------------------------------------------------ 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
