On Jul 5 2013 2:18 PM, Viesturs Lācis wrote: > 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.
you are correct. it is unfortunate that the character 4 is next to 3 and my fingers got ahead of my editing ;-) Seriously though, we should be able to merge Araisrobo's code and add spindle synchronized. >> 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.. sorry I did not explain it as well as you did. I also agree with the importance in general. My whole point was that smoothing higher order derivatives is a useful thing, and it is something I would like to see added (or merged from Araisrobo source). I was just piping up to make people aware who do not know about jerk. EBo -- ------------------------------------------------------------------------------ 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
