On Tuesday 01 May 2012 20:11:15 Kenneth Lerman wrote: > My understanding of the goal is that it is to have a minimum time > subject to certain constraints. > > The current constraints in LinuxCNC are to have certain acceleration and > velocity limits. It has been suggested that it would also be appropriate > to limit the jerk. Doing so could only make the time longer. This is not allway true.
It is true for stiff mechanics. The lowest resonant freuquency is _much_ higher compared to the exitation frequencies. In this case it makes no sense to reduce the acceleration. It is wrong for example for a gantry setup (2 y-axes). http://wiki.linuxcnc.org/cgi-bin/wiki.pl?FiveAxisGantry The traverse acts like a spring (bends) and the z-axis as a mass: -> a low frequency mechanical vibration is possible. With an unlimited jerc a movement of the 2 y-axes induces a frequency spectrum. If the 5th harmonic stimulates this mechanical resonance and the resulting vibration is not tolerable it is recommanded to reduce the amplitude of the high harmonics. With a jerk=f(t) it is possible to increase the acceleration because the higher frequency components are low in amplitude and do not stimulate machanical resonances. But the higher frequency components with low amplitude are always present. Good mechanics has some damping! > For a > variety of reasons (smaller error, less vibration, ...), some commercial > machines add such constraints. > > I suggest that if enhance LinuxCNC to add the jerk constraints, that > will be sufficient to "compete" with commercial solutions. This depends on the mechanical setup. > =============== > > I've noticed that most of the papers I've looked at seem to discuss the > problem of moving a single axis. Presumably, changing this to an N-axis > solution is straight forward. LinuxCNC, though, handles both linear and > circular interpolation. I've never looked closely enough at the design > to understand how circular interpolation would change the problem. > > Regards, > > Ken > Joachim ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
