It is fairly straightforward to plan a trajectory for a *single* segment (line, arc, nurbs-curve) with limited acceleration/jerk/double-jerk etc.
It is much harder to come up with an algorithm that blends together *many* lines/arcs/nurbs-curves and plans a smooth trajectory. Note that it is always necessary to deviate from the programmed path at the corners between segments (unless your CAM-program produces c2/c3/c4 continuous toolpaths!). So there is always a tolerance to be specified for blending. Better trajectory control for linuxcnc is a fairly hard problem to tackle. It's especially hard if we want to support arbitrary kinematics and feed-override settings. I think it would be wise to start with only trivial kinematics and no >100% feed-override allowed. Are there software tests for the trajectory controller? If so, has anyone run them on the araisrobo nurbs-branch (github)? Good tests would make it easier to develop something new and increase the confidence in new code before starting to move heavy metal. Anders On Mon, Jul 8, 2013 at 12:11 PM, EBo <[email protected]> wrote: > I never ment to imply that NURBS were necessary -- I like them for > other reasons (like exact representation of conics, splaying the control > polygon gives you a helix in closed form (read threading in any > arbitrary axis), is a natural representation produced from 3D models and > CAD systems, and of course the ability to smooth and analyze them. I > will take a look at the TinyG firmware for reference, and I am aware > that there are a number of ways to get to achieve jerk minimization. > > Thanks for the TinyG pointer BTW, > > EBo -- > > On Jul 8 2013 12:51 AM, Alexey Starikovskiy wrote: > > There is an quite simple algorithm, which is used in TinyG firmware. > > There > > is a link to the paper from their github. No NURBS involved. > > > > > > On Mon, Jul 8, 2013 at 1:23 AM, EBo <[email protected]> > > wrote: > > > >> Since I do not have my references handy I thought I would review > >> some > >> of the properties necessary to geometrically minimize jerk. I found > >> a > >> couple of references online that might make for a good read: > >> > >> > >> Smooth trajectory generation for five-axis machine tools: > >> > >> > >> > >> > http://academia.edu/3862221/Smooth_trajectory_generation_for_ve-axis_machine_tools > >> > >> So it looks like they are requiring C3 continuity, and uses NURBS. > >> This might comtinue the interesting debate... > >> > >> EBo -- > >> > >> > >> > >> > ------------------------------------------------------------------------------ > >> This SF.net email is sponsored by Windows: > >> > >> Build for Windows Store. > >> > >> http://p.sf.net/sfu/windows-dev2dev > >> _______________________________________________ > >> Emc-developers mailing list > >> [email protected] > >> https://lists.sourceforge.net/lists/listinfo/emc-developers > >> > > > > > ------------------------------------------------------------------------------ > > This SF.net email is sponsored by Windows: > > > > Build for Windows Store. > > > > http://p.sf.net/sfu/windows-dev2dev > > _______________________________________________ > > Emc-developers mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by Windows: > > Build for Windows Store. > > http://p.sf.net/sfu/windows-dev2dev > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers > ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
