2013/7/5 EBo <e...@sandien.com> > > > With LCNC-3.0 I would also like to see if we can add minimization of > jerk (the 4'th order derivative of position, so you end up taking the > derivative of acceleration and smooth it).
I do not want to be the smart-pants, but velocity is 1st, acceleration is 2nd and jerk is 3rd derivative of position. Anyway, it is already in Araisrobo code, AFAIK their code lacks spindle synchronized motion. > This is important for VERY > LARGE machines. I first learned about it from one of the technicians > who help build the VLA, and when you are moving a 3 story tall antenna > that is something like 25 meters across you cannot drive it without > acceleration, and you will tear up the bearings if you do not minimize > jerk... > Not only _very_ large machines. One beautifule example of unlimited jerk is: when driving car and you need to stop, press brake pedal with certain force (does not matter, how much, but the stronger you press it, the more obvious it is to understand) and hold it like that until the the car _completely_ stops. And pay attention to the moment, when car stops - velocity reaches zero, acceleration from negative number immediately jumps to zero (jerk is very large, if not infinite) and the feeling is as if you are kicked back in the seat. The same happens also in cnc machines - in moments, where acceleration changes to/from zero, accelerating/decelerating force is either removed or applied instantaneosly - just as if it was hit by hammer. And I just came up with a theory that jerk-limited motion would actually allow to push stepper performance higher as servos can recover from any position error, but stepper simply will lose steps in these moments.. -- Viesturs If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
