Sebastian Kuzminsky <s...@...> writes: snip...
> The hostmot2 encoder driver has a good velocity estimator, with the > value available on the .velocity-fb pin. I believe (though i dont know > for sure) that the older hostmot (aka m5i20) driver does *not* export > encoder velocity, so with that driver velocity has to be estimated using > additional HAL components (like ddt), which won't give as good a result. > > However... The current PID implementation in EMC2 does its own velocity > estimation (controlled via the feedforward gain), and can not accept > velocity information from outside itself. > > There are other reasons you might want good velocity feedback from your > encoders, but better PID control is not yet one of them. Maybe in 2.4 > Sebastian, Stephen, Peter, John, Jon - Thank you all for the volumes of information. I have read everything carefully - most several times - and followed all of the links and images. btw (John K.) - I have a printout right here on my desk from Anders Wallins' web page on PID tuning that I have used as my guide during the EMC2 conversion. Thanks for the pointer. As a result of your generous feedback I have put together a plan to fix the problem: ergo - ` Upgrade the encoders to 2000 line (8000 ppr) With 5 turn/inch ballscrews this will get me in the range of 10 encoder counts per .0004" - since I am using the Mesa 5i20 I can still have reasonably fast rapids on a fast host computer. ` Adjust the servo period to a smaller value, test for latency issues. ` Using halscope, adjust PID loop for lowest FERROR with attention to the FF1 & FF2 to minimize accel/decel errors, then back off on D term and/or increase deadband to improve stability (noise) at rest. ` Set FERROR & MIN_FERROR to prevent erroring out. ` Wait patiently for a "PID2" for EMC2 that hopefully gets incorporated into the Head. ` If so, then download and compile the latest Head version of EMC2, upgrade to Hostmot2, make the necessary adjustments to my ini & hal files and enjoy a smoother PID loop. Tom ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
