Looking at schematics or equations at https://en.wikipedia.org/wiki/Armature_Controlled_DC_Motor for a DC motor it could be seen armature voltage may be changed instantly while current take some time to change because of inductance in rotor marked "L rotor". To change motor speed require torque which depend on armature current while position is intergration of velocity. Acceleration depend on torque which depend on current so derivative of acceleration depend on derivative of current which may be controlled by voltage, this should conclude jerk may be changed instantly but then there are imperfections in real system.
If I remember it correct there is motion profiles in CANopen standard CiA417 called jerk limited ramp there jerk could be changed instantly and this should correspond to what is possible to achieve according to electric motor equation, elasticity in drive line will add further smoothnes. There is also something about it in CANopen standard CiA402, it is stated velocity is a third degree polynomial for both jerk free ramp and jerk limited ramp so jerk is a linear function and only difference I find between them is there is a maximum limit on jerk. At least me need to read them carefully, last time I might have intepreted figures wrong so numbers did not added up. Oddly enough I expect some elasticity in CiA417 which is for elevators so jerk free ramp is what is possible to achieve according to equations while jerk limited ramp as in CiA 417 as a second option would make sense in CiA 402 which is for servo motors. Nicklas SB Karlsson > A couple of sources: > http://www.mesanet.com/pdf/motion/softdmc.pdf 50 us cycle.... -:) > > Some years ago a masters candidate in ME at UBC did her thesis on motion > control with jerk limiting and sine wave accel. I used to have a copy of > it but cannot find it. > IIRC is would be post 2005 and author's name was something like Silvia > M(a)cFarland. > On the one axis motion controller what cycle time were you using and did > faster cycle times smooth it any? > > Dave > > On 7/22/20 1:51 PM, andrew beck wrote: > > hey guys > > > > I have a relatively high speed machine (3kw motors 16mm pitch ballscrews) > > 35mm linear rails, and weights 5.8 ton. I think it used to go 20m/min > > with the heidenhain control. I have been noticing a bit of jumping around > > when doing parallel finishing 3d passed on it at high speed. and talked to > > a couple of linuxcnc guys and found out that linuxcnc doesn't have any jerk > > control. just sending out a email here seeing what the current progress is > > on that. > > > > at high speed high precision linuxcnc definitely needs some work at some > > stage. > > > > apart from this I am completely happy with linuxcnc. this would be a nice > > thing to solve though. and if someone with the right skills wanted to fix > > it I would be happy as to chip in to pay something for the time. as I run > > a business in my machine shop where everything runs linuxcnc > > > > in the mean time I will try to get around the issue by programming in cam > > > > regards > > > > Andrew _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
