dave wrote: > Any progress on filtering D? Some commercial PID's apparently allow one > to adjust rolloff on D. > I've never found D or I as useful as I hope they are. If I can't fix it > with P, FF1 and FF2 then I probably won't be able to fix it. I suspect > the accel and decel spikes cannot really be fixed on systems with > backlash. I've never had a system tight enough to prove that. ;-) > If you have backlash between the motor and the encoder, such as with a worn leadscrew and a linear encoder, then you are dead! That is an intractable problem. The only fix is to move the encoder to the motor (still have backlash, but at least it doesn't go crazy) or fix the ballscrew (proper way to go.)
If the encoder is on the motor or the end of the leadscrew, that is at least tractable, but there will be a bump when the motor rotation takes up the backlash and suddenly starts to move the table. This won't cause incessant hunting, but it will surely cause a perturbation when that backlash is taken up. A bit of D definitely allows you to turn the P gain higher, but it also amplifies the quantizing effect of the encoder sampling. One way to fix this is to go to much higher encoder resolutions. I've been using a resolution of 128,000 counts/inch with good results. Jon ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
